Methods of and apparatus for making insulated multiconductor wire



1957 G. E. HENNING ETAL 2,778,059

METHODS 0 8 FOR MAKING F AND APPARATU SULATED MULTICONDUCTOR WIRE 4 INOriginal Filed Feb. 5, 195 2 Sheets-Sheet 1 /00:D 1 93 99 1' 92 I I /0464 I, 95

'O IO*I 9 F/G. 6 A. S. W/NDELER A TTORNEP .94 qt INVENTORS 9- G. CHENN/NG Jan. 22, 1957 HENNING EI'AL 2,778,059

G. E. METHODS OF AND APPARATUS FOR MAKING INSULATED MULTICONDUCTOR WIREOriginal Filed Feb. 3, 1954 2 Sheets-Sheet 2 a I INI/ENTORS c. 5 HENN/NCA. s. W/NDELER ATTORNEY fQS n ted? MuTnons OF AND APPARATUS FOR MAKINGINSULATED MuLrrcoNnucron WIRE 7 Claims. (Cl. 18-13) This inventionrelates to methods of and apparatus for making insulated multiconductorwire.

This application is a division of our copending application Serial No.407,872, filed February 3, 1954.

In the production of multi'conductor wires by extruding a commoninsulating covering of an insulating compound on a plurality of spacedconductors, serious difiiculties have been encountered in maintaininguniform the thickness of insulation between the individual conductorsand also between the conductors and the outer periphery of theinsulating covering. One of the principal causes of nonuniformity ininsulation thickness is the inadvertent presence of unbalanced plasticflow conditions in the extruding head of an extruder employed to formthe insulating covering. This problem is especially acute when theextruder employed is of the cross-head type having a transverseextruding head. This is due to the fact that in this type of extrudingapparatus there is an abrupt change in the direction of flow of theinsulating compound as it is forced into an extrusion passage in theextruding head.

In a typical cross-head type extruder which is provided with atransverse extruding head, the extrudable plastic material is forced bya stock screw into the extrusion passage in the head. Because of the 90bend in the flow path of the insulating compound, the length of: thepath traversed by the compound flowing through that portion of the crosssection of the extrusion passage closest to the stock screw issubstantially shorter than that traversed by the compound flowingthrough the opposite portion thereof, which is furtherest from the stockscrew. Also the flow of the compound through the portion of the crosssection of the passage closest to the stock screw approximates that of afluid bounded by a single plate, whereas in the other portion of thecross section furtherest from the stock screw, the flow approximatesthat of a fluid passing between two parallel plates. Hence, the frictionlosses in the portion nearest to the stock screw are appreciably lowerthan elsewhere in the passage.

As a result of the difference in the lengths of the paths traversed bythe insulating compound in various portions of the extrusion passage andthe characteristics of their associated flows, there exists asubstantial difference in the pressure heads at the critical point wherethe compound initially envelops the conductors in an extrusion diepositioned at the exit end of the extrusion passage. This imbalance ofpressure heads and resultant unbalance of plastic flow conditionsthroughout the cross section of the extrusion passage at the criticalpoint of extrusion causes eccentricity of the covering extruded on theconductors, the thinnest portion of the covering occurring in that partof the insulation produced in the portion of the passage cross sectionfurther-est from the stock screw (i. e. where the lowest pressure headexists).

Various schemes have been developed for eliminating these unbalancedplastic flow conditions in the extruding atent 2,778,059 Pa e 2: .9.5?

head. However, while some of these schemes have'be'en particiilarly"successful, none of them have succeeded in completely eliminating theunbalanced flow condition. Tlilis, in" practical applications it hasbeen found that there exists a certain ar'nou'nt of nonuniformity in thethickness of insulation between the individual conductors and the outerperiphery of the insulating covering. 7 This nonuniformity becomes aserious problem when the multiconductor wire so produced is designed foruse high frequency communication systems because of the resultantelectrical unbalance therein.

it is an o'bfect' of this invention to provide new and improved methodsof and apparatus for making insulated multiconductor wires.

A method illustrating certain features of the inverttion may include thesteps of advancing a plurality of conductors in spaced relationship,transposing' the spaced conductors rotatably as they are thus advanced,and simultaneously applying a common covering of insulating materialover the advancing conductors.

Apparatus illustrating certain features of the invention may include anextrusion head having an extrusion passage formed therein, arid aforming die mounted at the exit end of the extrusion passage. A memberis mounted for rotation about the longitudinal axis of the forming dieand is" provided with aplurality of longitudinal passages through whicha plurality of conductors may be advanced simultaneously into andthrough the forming die. Means are provided for turning the member totranspose the advancing conductors rotatably.

A complete understanding of the invention may be had from the followingdetailed description of methods of and apparatus for forming specificembodiments thereof, when read in conjunction with the appendeddrawings, in which:

Fig. l is a schematic diagran-rof an apparatus for mahufacturinginsulated multico'nductor wires;

Fig. 2 is a fragmentary, horizontal section of the apparatus taken alongthe longitudinal axis thereof, with parts thereof broken away forclarity;

Fig. 3 is an enlarged, vertical section taken along line 3-3 of Fig. 2;

Fig. 4 is an enlarged, fragmentary, perspective view of a portion of afinished multiconductor wire, with parts thereof broken away forclarity;

Fig. 5 is an enlarged, fragmentary view of a portion of the apparatusshown in Fig.2, and

Fig. 6 is a. schematic diagram of an electrical control circuitassociated with the apparatus.

Referring now in detail to the drawings, there is shown in Figs. 1 and 2an extruder 8 of the L-head type. As

shown in Fig. 2, the extruder 8 includes a stock screw 10 disposedlongitudinally for rotation within a cylindrical bore 11 of an extrusioncylinder 12 having a liner 13. Means (not shown) are provided forrotating the stock screw to knead and advance a plastic insulatingcompound 14 toward a delivery end of the extrusion bore 11, whereanextrusion head 15 is secured.

Mounted transversely across the delivery end of the extrusion bore 11 isa straining screen 16 supported upon a backing plate 1.8. After passingthrough the straining screen 16 and the backing plate 18, the plasticcompound 14- enters a tapered passageway 20 formed in a cylindrical.centrally apertured block 21. The entrance portion of the passageway 20diminishes gradually in cross section as it leads from the extrusionbore 11 to a passage 22 formed internally of the block 21. Thelongitudinal axis of the passage 22 is disposed transversely withrespect to the longitudinal axes of the bore 11 and the passageway 2i).

At the left-hand end of the passage 22, as seen in Fig. 2, is anextrusion die 24 mounted concentrically within an apertured retainingbushing 25 having an ex 3 ternal shoulder portion 26 and a counterbore27. The bushing is mounted fixedly within the left-hand end of thepassage 22 against a complementary shouldered portion 28 formed in thepassage.

Mounted concentrically within the passage 22 is a core tube holder 30which is provided intermediate of the ends with an externally threadedportion 32. The threaded portion 32 of the core tube holder 30 isreceived within an internally threaded axial bore 34 in an adapter plug35. The plug 35 is provided additionally with external threads whichpermit the plug to be secured threadedly within the extrusion head 15.As a result of this mounting arrangement, the core tube holder 30 isadjustable axially Within the passage 22.

' As shown in Fig. 2, the left-hand end of the core tube holder 39, inits normal position, extends into the counterbore 27 formed in thebushing 25. A transversely fiat face 37 provided on the left-hand end ofthe core tube holder 39 abuts the die 24. This end of the core tubeholder 30 is provided additionally on its external surface with aplurality of longitudinal grooves 39-39 which are spaced equally aboutits periphery. The longitudinal grooves 39-39 lead to a plurality ofradial grooves 40-4!) formed in the face 37 (Fig. 3). Thus, the lefthandend of the core tube holder 30 occupies all of the remaining portion ofthe counterbore 27 adjacent to the die 24, except for the space providedby the longitudinal grooves 39-39 and the radial grooves 40-40. As shownin Fig. 2, the longitudinal grooves 39-39 extend along the periphery ofthe core tube holder 30 from the left-hand end thereof to a point incommunication with the unoccupied portion of the passage 22 between theadapter plug 35 and the bushing 25.

. The core tube holder 30 is provided with an axial, cylindrical borewhich is provided with a counterbore 47 at the left-hand end thereof.Mounted rotatably Within the bore 45 and counterbore 47 in the core tubeholder 30, is a core tube 59, the external surfaces of which arecomplementary to the bore and counterbore, so as to fit closelytherewithin with a minimum of clearance provided to permit rotation ofthe core tube with respect to the core tube holder. The right-hand endof the core tube holder 3t? extends beyond the right-hand face of theadapter plug 35 and protrudes a substantial distance from the extrusionhead 15.

The right-hand end of the core tube 50 extends beyond the correspondingend of the core tube holder 30, and is provided at its extremity with aworm wheel keyed thereupon for rotation therewith. The worm wheel 60 isin meshing engagement with a worm 62 which is mounted on the shaft 63 ofa reversible electric motor 64. Energization of the motor 64 causesrotation of the worm 62, which rotation is transmitted to the core tube50 through the worm wheel 60.

. As shown in Fig. 2, the core tube 50 is provided with an axial borewhich extends the entire length thereof and is provided with acounterbore 72 at the left-hand end thereof. The counterbore 72 in thecore tube 50 is designed to receive a cylindrical insert 74 which whenpositioned in the counterbore fits tightly therewithin and is heldfixedly to the core tube for rotation therewith by means of a pin (notshown). The insert 74 is provided with four parallel, longitudinallyextending bores 77-77 spaced equally about the axis thereof, as shown inFig. 3. The left-hand end faces of the core tube ill and the insert 74are recessed slightly with respect to the face 37 of the core tubeholder 36.

The worm wheel 69 is provided with a lug 80 attached to the left-handface thereof at a point near its periphery. As the worm wheel 69 isrotated by the worm 62, the lug 86 travels in a circular path.Positioned adjacent to the path traveled by the lug 8b is a switch 32having a snapuction type actuator 83 placed so as to be contacted by thelug 83 each time the lug moves past the switch 82. The actuator 83 ismovable from side to side and when displaced suificiently to one side itwill snap into a more advanced position at that side.

Referring now to Fig. 6, which is a schematic diagram of a circuit forcontrolling the operation of the electric motor 64, when the actuator 33moves to the right with a snap-action it causes a contactor 85 to engagea contact 87. When the contactor 35 engages the contact 87, a solenoid92 of a solenoid-operated relay 93 is energized to close its associatedcontacts 94-94 and thereby to connect the motor to three-phase supplylines 95-95 which energize the motor 64 to rotate the shaft 63 in onedirection.

The contactor 85 will remain in engagement with the contact 87 until theactuator 83 is moved sufliciently to the opposite side by the lug 3% tocause it to snap into a position wherein the contactor 85 engages acontact 97. Before the contactor 85 engages the contact 97, itdisengages the contact 87.to break the circuit including the contact 37and the solenoid 2, causing the contacts 94-94 to drop out anddeenergize the motor. Then when the contactor 35 engages the contact 97,a circuit including a solenoid 99 of a solenoid-operated relay 100 iscompleted to close its associated contacts 162-102. The closing ofcontacts 102-102 energizes the motor 64- from supply lines $5-95 todrive the motor in a reverse direction. A manually operated switch 104is provided in the lines 95-95 for energizing and deenergizing thecircuit.

Operation Freparatory to an extruding operation, four individual,initially uninsulated, filamentary conductors -110 of copper wire, orthe like, are passed through the axial bore '70 in the core tube 5%,which is in axial alignment with the central orifice in the die 24. Theconductors 110- 119 are threaded individually through the bores 77-77 inthe insert 74, one conductor being positioned in each of the four boresso that the conductors passing from the core tube 50 into the orifice ofthe die 24 are disposed in an equilateral arrangement, as shown in Fig.3.

In operation, the conductors 110-110 are advanced continuously throughthe core tube 50 over a rotatable sheave 111 from individual supplies112-112 by means of a suitable capstan 113 driven by a motor 114. Theplastic compound 14 is worked and advanced continuously by the stockscrew 10 through the passageway 20 into the passage 22. Upon enteringthe passage 22, the flow of the plastic compound 14 is split up into aplurality of small streams which flow through the longitudinal grooves39-39, and thence through the radial grooves 40-40. The plastic compound14 flowing through the radial grooves til-4i) converges upon andenvelops completely the four individual, equilaterally spaced conductors110-110 as they exit from the bores 77-77 in the insert 74. The plasticcompound 14 forms a unitary conical stream as it enters the orifice ofthe die 24 and when the conductors 130-110 emerge from the exit end ofthe die, they are enveloped in a solidified, common sheath 115 ofinsulating compound to form a multiconductor wire (Fig. 4).

Although every effort is made to design and construct anextruding headin which there is a minimum of plastic flow unbalance, as a practicalconsideration, some unbalanced conditions always exist. Thus, it may beassumed that at the critical point of extrusion, where the plasticcompound 14 initially envelops the conductors 110-110, there exists asubstantial difference in the pressure heads of the flowing compound atdiiferent points throughout a cross section of the passage 22.

As the conductors 110-110 advance continuously through the bore 77-77 inthe insert 74, the core tube 50 and the insert are continuouslyoscillated rotatably through 360 about their longitudinal axis, theperiod of oscillation being determined by the speed of the motor 64. Themotor 64 rotates the core tube 50 and the insert 7-3 in one directionthrough an angle of 360, whereuponthe lug 80 engages and operates theactuator 83 to cause a reversal of the motor to rotate the core tube andinsert in the opposite direction through 360, whereupon the motor isagain reversed in a like manner.

The above-described oscillatory, rotational movement of the core tube 50and the insert 74 has the effect of spirally transposing the conductors110-410 with respect to the conical stream of plastic compound 14entering the orifice in the die 24 and enveloping the conductors, whilethe conductors remain in the same positions with respect to each other.As a result, each of the conductors 110-110 spirals about thelongitudinal axis of the insert 74. For example, assuming that thelinear speed of the conductors 110-110 is 150 feet per minute and thatthe speed of the motor 64 is such that it oscillates the core tube 50fifty times per minute, each convolution formed by the conductors willbe three feet in length.

In the finished multiconductor wire 120, the conductors 110110 are firstspiraled in one direction through 360 and then are spiraled in thereverse direction through 360", whereupon the cycle is repeated.Assuming that unbalanced plastic flow conditions exist at the criticalpoint of extrusion, each of the conductors 110-110 will continuouslymove through positions wherein it is covered alternately by a maximumand a minimum thickness of insulation, separating it from the outerperiphery of the sheath 115. Due to this transposition of the conductors110-110, one conductor will not always be in the position wherein thethickness of the insulation surrounding it is either a maximum or aminimum. Instead the diiferences in the thicknesses of the insulationsurrounding individual conductors 110-110 will be averaged out over along length of the multiconductor wire 120 and there will be a minimumof electrical unbalance inherent in such wire. Without theaforementioned transposition of the conductors the asymmetry caused byunbalanced plastic flow conditions would be systematic and even thoughit may be small it could build up to cause a sizable electricalunbalance in a cable length.

The term plastic insulating compound," as employed in this specificationand the following claims, will be understood to include boththermoplastic insulating compounds, such as polyethylene, or the like,and thermosetting insulating compounds, such as Neoprene compounds andother rubbery elastomers, or the like.

It will be understood that various modifications of the invention may bemade within the spirit and scope thereof.

What is claimed is:

1. The method of manufacturing insulated, multiconductor wires, whichcomprises simultaneously advancing a plurality of conductors in spacedrelationship, oscillating the spaced conductors rotatably as they arethus advanced, and simultaneously applying a common covering ofinsulating material over the advancing spaced, oscillating conductors,whereby variations in the covering of insulating material are uniformlydistributed along the length of the resulting composite product.

2. The method of manufacturing insulated, multiconductor wires, whichcomprises simultaneously advancing a plurality of spaced conductors,applying a common extruded covering of insulating material over theconductors, and simultaneously oscillating the conductors rotatablythrough a large angle, whereby variations in the thickness of theinsulation applied over individual conductors and in the spacing of theconductors are distributed over the length of the resulting compositeproduct.

3. The method of manufacturing insulated, multiconductor wires, whichcomprises simultaneously advancing a plurality of spaced conductors,applying a common extruded covering of insulating material over theconductors, and simultaneously oscillating the conductors rotatablythrough an angle of substantially 360, whereby variations in thethickness of the insulation applied over individual conductors and inthe spacing of the conductors are distributed over the length of theresulting composite product.

4. Apparatus for applying an extruded covering of a plastic materialupon a plurality of spaced conductors to form a composite, insulated,multiconductor wire, which comprises an extrusion head having alongitudinally extending extrusion passage formed therein, a forming diemounted at the exit end of the extrusion passage, a member mounted forrotation about the longitudinal axis of the forming die and providedwith a plurality of longitudinal guide passages through which aplurality of conductors may be advanced simultaneously into and throughthe forming die, and means for oscillating the member rotatably totranspose the advancing conductors.

5. In apparatus for applying a covering of plastic material upon aplurality of spaced conductors to form a composite multiconductor Wire,including a cross-head type extruder having an extruding head with anextrusion passage formed therein and a forming die mounted within theexit end of the passage, the improvement Which comprises a stationarycore tube holder mounted in the extrusion passage and provided with anaxial bore, a core tube mounted rotatably within the axial bore of thecore tube holder and provided with a plurality of passages through whicha plurality ofconductors may be simultaneously advanced into and throughthe die, and means operatively connected to the core tube foroscillating said core tube rotatably.

6. In apparatus for applying a covering of plastic material upon aplurality of spaced conductors to form a composite multiconductor wire,including a cross-head type extruder having an extruding head with anextrusion passage formed therein and a forming die mounted within theexit end of the passage, the improvement which comprises a stationarycore tube holder mounted in the extrusion passage and provided with anaxial bore, a core tube mounted rotatably within the axial bore of thecore tube holder and provided with a plurality of passages through whicha plurality of conductors may be simultaneously advanced into andthrough the die, and a reversible electric motor operatively connectedto the core tube for oscillating said core tube rotatably through arotational angle of substantially 360.

7. In apparatus for applying a covering of plastic material upon aplurality of spaced conductors to form a composite multiconductor wire,including a cross-head type extruder having an extruding head with anextrusion passage formed therein and a forming die mounted within theexit end of the passage, the improvement which comprises a stationarycore tube holder mounted in the extrusion passage and provided with anaxial bore, a core tube mounted rotatably within the axial bore of thecore tube holder and provided with a plurality of spaced longitudinalpassages, means for advancing a plurality of conductors simultaneouslyat a predetermined speed through corresponding passages in the core tubeand into and through the die, and means operatively connected to thecore tube for oscillating said core tube rotatably at a predeterminedrate through a rotational angle of substantially 360.

References Cited in the file of this patent UNITED STATES PATENTS1,797,249 Truesdale et al Mar. 24, 1931 1,984,038 Shaw et al. Dec. 11,1934 2,446,057 Morin July 27, 1948

